1. Field of the Invention
This invention relates to atomizers and, more particularly, to airblast atomizers used in combustors for gas turbine engines.
2. Description of the Prior Art
The use of air to atomize liquids, such as fuel for combustion in gas turbines, is well known and the methods employed vary widely depending on the desired results, which are influenced by the fineness of atomization, the properties of liquid fuel, the availability of air for the atomizing process and the homogenity of the fuel/air mixture, referred to as F/A mixedness.
For example, where compressed air can be supplied from an external source, a device such as that disclosed in U.S. Pat. No. 3,474,970 can be employed, in which high velocity air is applied to one side of a conical fuel sheet produced by the discharge of a conventional spin-chamber or xe2x80x9cSimplexxe2x80x9d nozzle and flowing on the interior surface of a cone. The application of this principal, however, is limited to relatively low fuel flow rates, and the nozzle operates on a conventional fuel pressure atomizer at a high flows produced using compressed air. In certain applications the use of compressed air is not feasible and is preferred to employ the air which is fed into the combustion chamber from the engine compressor to atomize the fuel. This method is disclosed in U.S. Pat. No. 3,283,502 which describes generally spreading the fuel into a thin film on the surface and atomizing the fuel sheet as it leads the edge of the surface. U.S. Pat. No. 3,530,667 also shows the fuel being spread over a relatively large surface, developing a thin sheet of fuel, for ease of mixing with air, with the air being applied to both sides of the fuel sheet leaving the edge of the surface. Such fuel nozzles are described as the xe2x80x9cprefilmingxe2x80x9d type. In both of these cases, it is evident that the success of the atomization process can be effected by the behavior of the liquid film since in general the size of the atomized drop produced is dependent on the thickness of the fuel film at the point of breakup. Variations of fuel film thickness can occur for various reasons, and this could give rise to poor atomization performances. Optimum atomization of the fuel/air mixture is important in controlling the flame temperature during combustion. The highest source of NOx is a high flame temperature. Maintaining a homogeneous fuel/air mixture (good mixedness) prior to combustion provides a much higher level of control for a desired flame temperature.
An atomizer is desired that will promote uniform atomization of a homogenous fuel/air mixture for combustion, thereby promoting low micron-size fuel particles and allowing closer control of the flame temperature, which in turn produces a more efficient engine cycle while at the same time minimizing the level of undesirable NOx and other emission species
One embodiment of the subject invention is directed to an atomizer for use with a combustor in a gas turbine, wherein the atomizer is comprised of:
a body;
fuel passageway within the body extending along a passageway centerline, wherein the fuel passageway has an entry end and a discharge end; and
a plurality of channels extending within the body about the passageway centerline and spaced around the discharge end of the fuel passageway, wherein at the discharge end of the passageway the channels are oriented along a circumferential angle about the passageway centerline to deliver air at the discharge end of the passageway centerline to deliver air at the discharge of the passageway with a whirling motion and wherein the channels are simultaneously oriented along an axial angle about the passageway centerline thereby converging toward the passageway centerline to deliver air at the discharge end toward the passageway centerline.
Another embodiment of the subject invention is directed to an atomizer for use with a combustor in a gas turbine, wherein the atomizer is comprised of:
a) providing a stream of fuel against a fuel passageway such that the fuel conforms to the wall of the passageway and exits in a shape conforming to the wall;
b) providing a flow of air which both rotates and diverges toward and intersects with the stream of fuel thereby atomizing the stream of fuel.
A third embodiment of the subject invention is directed to an annular combustor comprising:
a) a combustion chamber;
b) at least one atomizer for receiving and mixing fuel and air for introduction to the combustion chamber;
c) wherein the atomizer is comprised of
1) a body,
2) a fuel passageway within the body extending along a passageway centerline, wherein the fuel passageway has an entry end and a discharge end; and
3) a plurality of channels extending within the body about the passageway centerline and spaced around the discharge end of the fuel passageway, wherein at the discharge end of the passageway the channels are oriented along a circumferential angle about the passageway centerline to deliver air at the discharge end of the passageway with a whirling motion and wherein the channels are simultaneously oriented along an axial angle about the passageway centerline thereby converging toward the passageway centerline to deliver air at the discharge end toward the passageway centerline.